Many classes of polyamide resins, commonly referred to as nylon, are known. One class of such polyamides is ordinarily obtained by a polycondensation reaction between a polybasic acid and a polyamine. For instance, the polycondensation reaction between adipic acid and hexamethylene diamine yields polyhexamethylene adipamide which is commonly referred to as nylon 66. Such polyamide resins in the form of shaped objects have been found to be useful in numerous applications, e.g., flexible tubing. A principle disadvantage and drawback of the polyamide resins is the lack of resistance to degradation occasioned by contact with zinc chloride. Specifically, exposure to zinc chloride will result in deterioration and degradation of shaped articles molded from polyamide resins as evidenced by extensive cracks that appear and form throughout such shaped articles. It has been observed that resistance to zinc chloride appears to be related to the number of carbon atoms of the amide group in the polymer chain. That is, the resistance to zinc chloride increases as the number of carbon atoms between each pair of repeating amide groups of the polymer chain increases. To illustrate, nylon 6 and nylon 66 are more sensitive to zinc chloride than nylon 612 which is, in turn, more sensitive than nylon 11 and nylon 12. Attempts have been made to increase the zinc chloride resistance of polyamide resins. For example, British Patent Specification No. 1,367,840 describes a polyamide copolymer having increased zinc chloride resistance that is obtained by copolymerizing from 0.5 to 15% by weight of a dimerized salt of the formula EQU HOOC--R--COOH.H.sub.2 N--R'--NH.sub.2
wherein R and R' are saturated hydrocarbon radicals having from 25 to 50 carbon atoms and a polyamide-forming monomer. Long carbon-chain salts such as the foregoing and long carbon-chain dicarboxylic acids and lactams used heretofore to provide zinc chloride-resistant polyamides are, however, quite expensive. Accordingly, it is the principal object of the present invention to provide specific polyamide resins that are zinc-chloride resistant and more economical.